1. Field of the Invention
The present invention relates to a control device of an automatic transmission for vehicles.
2. Description of the Prior Art
An example of conventional automatic transmission comprises a main transmission arranged coaxially with a torque converter and having planetary gear mechanisms, and a sub transmission arranged in parallel with the main transmission. The control device of the automatic transmission achieves a plurality of gear positions by engaging and disengaging friction elements such as clutches, brakes and one-way clutches.
In this type of control device, an automatic transmission control unit (hereinafter referred to as an ATCU) determines a gear position suitable for driving conditions, and on-off controls solenoid valves in the control device. The gear positions are changed by supplying and releasing an oil pressure supplied through the solenoid valves to and from friction elements by an oil pressure circuit comprised of shift valves and the like.
In the control device that is constructed in the above-mentioned manner, if there is a problem in the ATCU or the like, it is impossible to control the solenoid valves for determining the gear positions, and therefore, the gear position may be fixed at a specific gear position.
To address this problem, the oil pressure circuit in the conventional control device of the automatic transmission is constructed in such a manner that the gear position shifts to an intermediate gear position or a low speed gear position in order to insure a driving performance after the problem occurs.
In recent years, however, the number of gear positions have been increased so as to control a driving characteristic in a more refined manner in order to reduce energy consumption and the like. An automatic transmission with five gear positions has already been developed, and an automatic transmission with six gear positions is now being studied.
Accordingly, while a vehicle is driven at the high speed gear position such as the sixth speed gear position or the fifth speed gear position, if a problem occurs and the high speed gear position is shifted to an intermediate gear position such as the third speed gear position or a low speed gear position such as the second speed gear position, the abrupt down-shift may cause deterioration of the driving performance.
In order to prevent the gear position from shifting to the intermediate gear position or the low speed gear position, the control device may be constructed in such a manner that the gear position is shifted up to a highest speed gear position irrespective of the present gear position when there occurs a problem, In this case, however, the driving performance may deteriorate if the gear position is abruptly shifted up to the highest gear speed while a vehicle is driven at the low speed gear position.
It is therefore an object of the present invention to provide a control device of an automatic transmission, which prevents the deterioration of driving performance even if there is a problem during driving.
According to the first aspect of the present invention, the control device of the automatic transmission, which comprises a plurality of gear position selecting signal pressure generating means that supplies and releases signal pressure for controlling engagement and disengagement of a plurality of friction elements, and shift control means that controls the gear position selecting signal pressure generating means according to gear positions selected by an automatic shift or a manual shift in order to achieve a plurality of forward driving gear positions by engagement and disengagement of the plurality of friction elements, is characterized in that:
the plurality of forward driving gear positions comprises at least a low speed gear position group composed of multiple forward driving gear positions including a lowest speed gear position and a high speed gear position group composed of multiple forward driving gear positions with higher speeds than the low speed gear position group;
the plurality of gear position selecting signal pressure generating means generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the low speed gear position group, when the shift control means stops functioning; and
the control device of the automatic transmission comprises:
high speed gear position signal pressure generating means that generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the high speed gear position group;
low speed gear position failsafe means that supplies the friction elements which are engaged at the predetermined gear position in the low speed gear position group with the signal pressure generated by the gear position selecting signal pressure generating means if the shift control means stops functioning when the shift control means selects a gear position in the low speed gear position group; and
high speed gear position failsafe means that supplies the friction elements which are engaged at the predetermined gear position in the high speed gear position group with the signal pressure generated by the high speed gear position signal pressure generating means if the shift control means stops functioning when the shift control means selects a gear position in the high speed gear position group.
Accordingly, if the shift control means stops functioning while a vehicle is driven at a gear position in a low speed gear position group, the low speed gear position failsafe means supplies the friction elements with the signal pressure outputted from the gear position selecting signal pressure generating means. When the shift control means stops functioning, the gear position selecting signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at a predetermined gear position in the low speed gear position group. Thus, a predetermined gear position in the low speed gear position group is engaged.
If the shift control means stops functioning while the vehicle is driven at a gear position in the high speed gear position group, the high speed gear position failsafe means supplies the friction elements with the signal pressure outputted from the high speed gear position signal pressure generating means. When the shift control means stops functioning, the high speed gear position signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at a predetermined gear position in the high speed gear position group. Thus, a predetermined gear position in the high speed gear position group is engaged.
Therefore, when the shift control means stops functioning, the gear position is fixed at the gear position at which the vehicle has been driven, or is switched to and fixed at a gear position in the same gear position group whether the vehicle is driven at a low speed gear position or a high speed gear position. This prevents the down-shift from the high speed gear position group to the low speed gear position group, or the up-shift from the low speed gear position group to the high speed gear position group, thereby preventing the deterioration of the driving performance.
According to the second aspect of the present invention, the control device of an automatic transmission, which comprises a plurality of gear position selecting signal pressure generating means that supplies and releases signal pressure for controlling engagement and disengagement of a plurality of friction elements, and shift control means that controls the gear position selecting signal pressure generating means according to gear positions selected by an automatic shift or a manual shift in order to achieve a plurality of forward driving gear positions by engagement and disengagement of the plurality of friction elements, is characterized in that:
the plurality of forward driving gear positions comprises at least a low speed gear position group composed of multiple forward driving gear positions including a lowest speed gear position and a high speed gear position group composed of multiple forward driving gear positions with higher speeds than the low speed gear position group;
the plurality of gear position selecting signal pressure generating means generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the low speed gear position group, when the shift control means stops functioning; and
the control device of the automatic transmission comprises:
high speed gear position signal pressure generating means that generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the high speed gear position group;
a failsafe valve that supplies the friction elements which are engaged at the predetermined gear position in the low speed gear position group with the signal pressure generated by the plurality of gear position selecting signal pressure generating means at a first switching position, and supplies the friction elements which are engaged at the predetermined gear position in the high speed gear position group with the signal pressure generated from the high speed gear position signal pressure generating means at a second switching position;
a high speed gear position storage valve that supplies and releases a high speed gear position storage signal pressure for controlling the switching positions of the failsafe valve;
a high speed gear position storage cancel valve that supplies and releases original pressure of the high speed gear position storage signal pressure to and from the high speed gear position storage valve;
abnormality sensing means that supplies the failsafe valve with a normal operation signal pressure when the shift control means is operating normally, and stops the supply of the normal operation signal pressure when the shift control means stops functioning;
wherein when the shift control means selects a gear position in a high speed gear position group, the high speed gear position storage valve supplies the high speed gear position storage signal pressure and stores the supplied state of the high speed gear position storage pressure by self-maintaining the switching state by the high speed gear position storage signal pressure, and if the shift control means stops functioning when the shift control means selects a shift position in a high speed gear position group, the high speed gear position storage valve continues supplying the high speed gear position signal pressure;
when the shift control means selects a gear position in the low speed gear position group, the high speed gear position storage cancel valve stops supplying the original pressure of the high speed gear position storage signal pressure to thereby cancel the self-maintenance of the switching state in the high speed gear position storage valve and cancel the storage of the supplied state of the high speed gear position storage signal pressure; and
if the normal operation signal pressure only is supplied or if neither the normal operation signal pressure nor the high speed gear position storage signal pressure is supplied, the failsafe valve is switched to a first switching position, and if the high speed gear position storage signal pressure is only supplied, the failsafe valve is switched to a second switching position.
While the vehicle is driven at a gear position in the low speed gear position group, the abnormality sensing means supplies the failsafe valve with the normal operation signal pressure, and the failsafe vale is switched to the first switching position.
If the shift control means stops functioning at this time, the supply of the normal operation signal from the abnormality sensing means is stopped. On the other hand, the high speed gear position storage valve does not supply the high speed gear position storage signal pressure to the failsafe valve. For this reason, the failsafe vale is not supplied with the normal operation signal pressure or the high speed gear position storage signal pressure, and the failsafe valve is fixed at the first switching position.
At the first switching position, the failsafe vale supplies the friction elements which are engaged at the predetermined gear position in the low speed gear position group with the signal pressure generated from the gear position selecting signal pressure generating means. Since the shift control means does not function normally, the gear position selecting signal pressure generating means generates the signal pressure to be supplied to the friction elements, which are engaged at a predetermined gear position in the low speed gear position group.
Therefore, the friction elements are engaged in such a manner as to select a predetermined gear position in the low speed gear position group.
Thus, if the shift control means stops operating normally while the vehicle is driven at a gear position in the low speed gear position group, the gear position is switched to and fixed at a gear position in the low speed gear position group.
While the vehicle is driven at a gear position in the high speed gear position group, the abnormality sensing means supplies the normal operation signal to the failsafe valve, which is switched to the first switching position. At this time, the high speed gear position storage cancel valve supplies the high speed gear position storage valve with the original pressure of the high speed gear position storage signal pressure. The high speed gear position storage valve supplies the failsafe valve with the high speed gear position storage signal pressure, and the high speed gear position storage valve self-maintains the switching state by the high speed gear position storage signal pressure. Since the abnormality sensing means supplies the failsafe valve with the normal operation signal pressure, the switching state of the failsafe valve is unchanged from the first switching state.
If, however, the shift control means stops functioning, the abnormality sensing means stops supplying the normal operation signal pressure. Thus, the failsafe valve is not supplied with the normal operation signal pressure. On the other hand, the high speed gear position storage cancel valve supplies the high speed gear position storage valve with the original pressure of the high speed gear position storage signal pressure, and thus, the high speed gear position storage valve supplies the failsafe valve with the high speed gear position storage signal pressure, and the high speed gear position storage valve self-maintains the switching state by the high speed gear position storage signal pressure. For this reason, the failsafe valve is only supplied with the high speed gear position storage signal pressure, and the failsafe valve is switched to the second switching position.
At the second switching position, the failsafe valve supplies the friction elements which are engaged at the predetermined gear position in the high speed gear position group with the signal pressure generated from the high speed gear position signal pressure generating means, and thus, the friction elements are engaged in such a manner as to select a predetermined gear position in the high speed gear position group.
Therefore, if the shift control means stops functioning normally while the vehicle is driven at a gear position in the high speed gear position group, the gear position is switched to and fixed at a predetermined gear position in the high speed gear position group.
When a gear position in the high speed gear position group is switched to a gear position in the low speed gear position group, the high speed gear position storage cancel valve stops supplying the original pressure of the high speed gear position storage signal pressure and cancels the self-maintaining state of the high speed gear position storage valve.
Therefore, if a gear position in the high speed gear position group is switched to a gear position in the low speed gear position group, the high speed gear position storage valve stops outputting the high speed gear position storage signal pressure.
For this reason, when the shift control means stops functioning, the gear position is fixed at a gear position at which the vehicle has been driven, or is switched to and fixed at a gear position in the same gear position group whether the vehicle is driven at a low speed gear position or a high speed gear position. This prevents the down-shift from the high gear position to the low speed gear position group, and the up-shift from the low gear position to the high speed gear position group, thereby preventing the deterioration of the driving performance.
According to the first and second aspects, the plurality of gear position selecting signal pressure generating means may generate the signal pressure to be supplied to the friction elements, which are engaged at the highest speed gear position in the low speed gear position group when the shift control means stops functioning.
Therefore, if the shift control means stops functioning while the vehicle is driven at a gear position in the low speed gear position group, the gear position selecting signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at the highest speed gear position in the low speed gear position group. Thus, the highest speed gear position in the low speed gear position group is engaged.
If down-shift occurs in the low speed gear position group, the great change of the driving performance is caused. However, in this embodiment the gear position is fixed at a gear position at which the vehicle has been driven, or is switched to and fixed at a higher speed gear position if the shift control means stops functioning while the vehicle is driven at a low gear position. Thus, there is no down-shift, and this prevents the deterioration of the driving performance more effectively.
According to the third aspect of the present invention, the control device of the automatic transmission, which comprises a plurality of gear position selecting signal pressure generating means that supplies and releases signal pressure for controlling engagement and disengagement of a plurality of friction elements, and shift control means that controls the gear position selecting signal pressure generating means according to gear positions selected by an automatic shift or a manual shift in order to achieve a plurality of forward driving gear positions by engagement and disengagement of the plurality of friction elements, is characterized in that:
the plurality of forward driving gear positions comprises at least a low speed gear position group composed of multiple forward driving gear positions including a lowest speed gear position and a high speed gear position group composed of multiple forward gear positions with higher speeds than the low speed gear position group;
the plurality of gear position selecting signal pressure generating means generates signal pressure to be supplied to friction elements, which are engaged at a highest gear position in the low speed gear position group, when the shift control means stops functioning; and
the control device of the automatic transmission comprises:
high speed gear position signal pressure generating means that generates signal pressure to be supplied to friction elements, which are engaged at a highest speed gear position in the high speed gear position group;
a failsafe shift valve that supplies the friction elements which are engaged at a highest gear position in the low speed gear position group with the signal pressure generated by the plurality of gear position selecting signal pressure generating means at a first switching position, and supplies the friction elements which are engaged at a highest speed gear position in the high speed gear position group with the signal pressure generated from the high speed gear position signal pressure generating means at a second switching position;
a high speed gear position storage shift valve that supplies and releases a high speed gear position storage signal pressure for controlling shift positions of the failsafe shift valve;
a high speed gear position storage cancel shift valve that supplies and releases original pressure of the high speed gear position storage signal pressure to and from the high speed gear position storage shift valve;
abnormality sensing means that supplies the failsafe shift valve and the high speed gear position storage cancel shift valve with normal operation signal pressure for controlling shift positions when the shift control means is operating normally, and stops supplying the normal operation signal pressure when the shift control means stops functioning;
high speed gear position selecting signal pressure generating means that supplies the high speed gear position storage shift valve and the high speed gear position storage cancel shift valve with high speed gear position selecting signal pressure for controlling shift positions when the shift control means selects a gear position in the high speed gear position group;
wherein the high speed gear position storage cancel shift valve supplies the high speed gear position storage shift valve with the original pressure of the high speed gear position storage signal pressure when both the normal operation signal pressure and the high speed gear position selecting signal pressure are supplied or when neither the normal operation signal pressure nor the high speed gear position selecting signal pressure are supplied;
the high speed gear position storage shift valve controls shift positions thereof by the high speed gear position storage signal pressure, and supplies the high speed gear position storage signal pressure to the failsafe shift valve when the high speed gear position selecting signal pressure and the original pressure of the high speed gear position storage signal pressure are supplied or when the supply of the high speed gear position selecting signal pressure is stopped in a state wherein the high speed gear position selecting signal pressure and the original pressure of the high speed gear position storage signal pressure are supplied; and
if the normal operation signal pressure only is supplied or if neither the normal operation signal pressure nor the high speed gear position storage signal pressure are supplied, the failsafe shift valve is switched to a first shift position, and if the normal operation signal pressure is not supplied and the high speed gear position storage signal only is supplied, the failsafe shift valve is switched to a second shift position.
Accordingly, while the vehicle is driven at a gear position in the low speed gear position group, the abnormality sensing means supplies the normal operation signal pressure to the failsafe shift valve, which is shifted to the first shift position.
If the shift control means stops functioning at this condition, the abnormality sensing means stops supplying the normal operation signal pressure. On the other hand, the high speed gear position storage shift valve does not supply the high speed gear position storage signal pressure to the failsafe shift valve or the high speed gear position storage shift valve itself. Therefore, the failsafe shift valve is fixed at the first shift position since the failsafe shift valve is not supplied with the normal operation signal pressure or the high speed gear position storage signal pressure.
At the first shift position, the failsafe shift valve supplies the friction elements with the signal pressure generated from the gear position selecting signal pressure generating means. Since the shift control means does not function normally, the gear position selecting signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at the highest speed gear position in the low speed gear position group.
Accordingly, the friction elements are engaged in such a manner as to select the highest speed gear position in the low speed gear position group.
Thus, if the shift control means stops functioning normally while the vehicle is driven at a gear position in the low speed gear position group, the gear position is switched to and fixed at the highest speed gear position in the low speed gear position group.
While the vehicle is driven at a gear position in the high speed gear position group, the abnormality sensing means supplies the normal operation signal to the failsafe shift valve, which is shifted to the first shift position.
At this time, the high speed gear position selecting signal pressure supplies the high speed gear position selecting signal pressure to the high speed gear position storage cancel shift valve, which then supplies the original pressure of the high speed gear position storage signal pressure to the high speed gear position storage shift valve.
The high speed gear position storage shift valve is supplied with the high speed gear position selecting signal pressure from the high speed gear position selecting signal pressure generating means, and is also supplied with the original pressure of the high speed gear position storage signal pressure. Thus, the high speed gear position storage shift valve supplies the high speed gear position storage signal pressure to the failsafe shift valve. The failsafe shift valve, however, is supplied with the normal operation signal pressure from the abnormality sensing means, and thus, the shift position of the failsafe shift valve is fixed at the first shift position.
If, however, the shift control means stops functioning, the abnormality sensing means stops supplying the normal operation signal pressure. For this reason, the failsafe shift valve is not supplied with the normal operation signal pressure. On the other hand, the high speed gear position storage shift valve is supplied with the high speed gear position selecting signal pressure from the high speed gear position selecting signal pressure generating means, and is also supplied with the original pressure of the high speed gear position storage signal pressure. Therefore, the high speed gear position storage shift valve supplies the high speed gear position storage signal pressure to the failsafe shift valve. Thus, the failsafe shift valve is only supplied with the high speed gear position storage signal pressure, and is shifted to the second shift position.
When the failsafe shift valve is shifted to the second shift position, the friction elements are supplied with the signal pressure generated from the high speed gear position signal pressure generating means. Accordingly, the friction elements are engaged in such a manner as to select the highest speed gear position.
Therefore, if the shift control means stops functioning normally while the vehicle is driven at a gear position in the high speed gear position group, the gear position is switched to and fixed at the highest speed gear position.
When a gear position in the highest speed gear position group is switched to a gear position in the low speed gear position group, the high speed gear position storage cancel shift valve stops supplying the original pressure of the high speed gear position storage signal pressure, and cancels the self-maintaining state of the high speed gear position storage shift valve.
Therefore, when the gear position in the high speed gear position group is switched to the gear position in the low speed gear position group, the high speed gear position storage shift valve stops outputting the high speed gear position storage signal pressure.
In one preferred mode of the present invention, when the shift control means stops functioning, all outputs thereof carry no current, and the abnormality sensing means is a normal low type solenoid valve that supplies no signal pressure when no current is carried.
The use of the normal low type solenoid valve makes it possible to stop the supply of the normal operation signal pressure with a simple circuit structure when the shift control means stops functioning and all the outputs carry no current. This enables the reduction in the cost.
Alternatively, when the shift control means stops functioning, all outputs thereof carry no current; and the plurality of gear position selecting signal pressure generating means comprises normal high type solenoid valves, which supplies oil pressure in a state wherein no current is carried, and normal low type solenoid valves, which supply no signal pressure in a state wherein no current is carried; and the normal high type solenoid valves generate signal pressure to be supplied to the friction elements, which are engaged at the highest speed gear position in the low speed gear position group.
This enables the supply of the signal pressure to be supplied to the friction elements, which are engaged at the highest speed gear position in the low speed gear position group, with a simple circuit structure when the shift control means stops functioning and all the outputs carry no current. This enables the further reduction in the cost.